I'm looking for a specific fic that I am so sure I saved, so either I'm bad at looking through my bookmarks, or it's deleted.
Ok, here we go.
Sam is at Stanford and Dean and John are still hunting together. I think they were hunting a witch and it's her who cruses Dean. The curse is that whenever you think of someone you miss a lot, you get hurt. So of course for Dean it's Sam. So whenever he thinks about him or starts talking about him, I think he gets these seizure-like things and starts bleeding nose blood and is just in a lot of pain.
Once it happens at a diner and dean is writhing on the floor in pain and john is freaking out. He talks to him and finally John's voice gets through to Dean and he manages to snap out of it. John is really worried and eventually he calls Sam, when he figures out what's going on, and Sam comes to their hotel and when Dean sees him, he gets better.
That's what I remember.